1. Field of the Invention
This invention relates to a connector secured, for example, to a cable installed in a vehicle such as an automobile.
2. Related Art
Various electronic equipments such for example as a navigation system are mounted on a vehicle such as an automobile. Cables each comprising a plurality of wires are installed in the vehicle so as to supply electric power to these electronic equipments and also to transmit signals between the electronic equipments. A connector for connection to a connector of the electronic equipment is secured to the cable.
For example, the above navigation system comprises a body portion for calculating a present position of the vehicle, and a display for indicating the present position of the vehicle and the position of a destination, and the body portion and the display are connected together via a cable. In recent years, the display has been required to have high resolution, and also has been required to display the present position of the vehicle in real time, and therefore it has become necessary to transmit a large amount of signals between the body portion and the display at high speed.
There are two types of conventional high-speed transmission methods, that is, an unbalanced (single-end) type and a differential type. In the unbalanced type, one signal wire is used for each signal path, and a grounding wire is common to the signal paths, and a voltage of each signal wire relative to the grounding potential is transmitted as a signal. On the other hand, in the differential type, two signal wires are used for each signal path, and a voltage difference between the two wires is transmitted as a signal. In the differential type, voltages of the two wires are equal in magnitude to each other, and are 180° out of phase with each other, and the differential type does not respond to a signal (such electromagnetic noises) evenly applied to the two signal wires, and therefore the differential type has a feature that it is resistant to noises, and therefore is suited for high-speed transmission.
The Applicant of the present application has earlier proposed a connector used for such differential type transmission, which connector includes a plus signal terminal and a minus signal terminal for connection respectively to two wires (For convenience' sake, one is for a plus signal, and the other is for a minus signal) of a cable, and a ground terminal for connection to a grounding wire of the cable (see, for example, JP-A-2003-100399).
The cable to which the connector of JP-A-2003-100399 Publication is secured includes the plus signal wire, the minus signal wire, and the grounding wire. The plus signal wire, the minus signal wire and the grounding wire are arranged parallel to one another, and are disposed in a triangle pattern (that is, disposed respectively at apexes of a triangle) in a transverse cross-section of the cable perpendicular to a longitudinal axis of the cable.
Here, impedance match is achieved between the cable, the connector of the cable, and the connector of the electronic equipment. If impedance mismatch is encountered, reflection of the signal occurs at such a mismatching region, so that the proper transmission can not be effected. Particularly when transmitting a large amount of signals at high speed, the impedance need to be strictly matched.
Therefore, in the connector disclosed in JP-A-2003-100399, the plus signal terminal, the minus signal terminal and the ground terminal are arranged in a triangular pattern (that is, disposed respectively at apexes of a triangle) as is the case with the arrangement of the wires of the cable to which these terminals are connected. With this arrangement, the relative positional relation of the signal path (that is, the wires and the terminals connected to the respective wires) is generally constant over the entire range including the cable and the connector, and therefore impedance match between the connector and the cable is enhanced.
In recent years, connectors have been required to have a compact or small-size design, and in order to meet this requirement a gap between adjacent terminals tends to be reduced. It is known that the gap between the adjacent terminals, a dielectric constant of an insulator (that is, a synthetic resin forming a connector housing) disposed between the terminals, etc., are related to the impedance of the connector.
In this respect, in a connector of a conventional structure such as the connector of JP-A-2003-100399 Publication, the impedance can be matched by suitably changing a connector housing-forming synthetic resin. Namely, a synthetic resin of a lower dielectric contact is used as the synthetic resin for forming the connector housing, and by doing so the impedance match which is lowered by the reduced gap between the terminals due to the compact design of the connector can be maintained at a conventional level. Among various synthetic resins, for example, teflon has an extremely low dielectric constant, and is suitable for forming the connector housing.
However, when a different synthetic resin is used for each connector, it is feared that the production cost of the connector increases. Furthermore, when connectors become increasingly compact in design, it is thought that it is difficult to obtain impedance match even with the use of teflon, and besides teflon is relatively expensive.
Soldering is often used as joining means for electrically connecting a terminal to a wire. In this case, the synthetic resin, forming the connector housing, is required to have heat resistance. There is known the type of synthetic resin having glass fibers or the like mixed therein in order to enhance the heat resistance. However, usually, the dielectric constant tends to be increased by such additive. Therefore, even when the connector housing-forming synthetic resin is suitably changed, this synthetic resin is limited to a special one having excellent heat resistance and a low dielectric constant.